After the local elections, Jeremy Corbyn has passed a peak, but he could climb back up again

He will have been Labour leader for seven years by the time of the next election: can he find new ways to be the comeback kid?

There have been some bad assessments of this week’s English local elections. One of the worst was by Boris Johnson, who said that Theresa May’s “clear Mansion House vision for leaving the single market and customs union” was “a key part of Tory electoral success”.

The foreign secretary claims that the voters of Basildon, Peterborough and Redditch, where the Conservatives gained control, or of Derby and Nuneaton, where Labour lost it, went to the polls saying to themselves that they must stop the prime minister’s plan to collect tariffs on behalf of the EU.

The absurdity is a clue to Johnson’s desperation. As was his excitement when he realised there was a majority in the cabinet Brexit committee on Wednesday against May’s customs compromise. According to Gary Gibbon, Channel 4 News political editor, Johnson blurted out, when everyone on the 11-member committee had spoken: “That’s six-five, it’s six-five … let’s have a vote.”

The foreign secretary knows there is a majority in parliament in favour of a customs union. Hence his desperation to suggest that Tory successes in Leave areas are votes for a hard rather than soft Brexit. As Professor John Curtice wrote for The Independent yesterday, the British political map is realigning as the Tories become more the party of Leave and Labour more that of Remain, but this has little to do with the technical details of customs arrangements.

Another bad assessment of the local elections was the theme of many of Jeremy Corbyn’s supporters on social media: that he would be prime minister if Thursday had been a general election.

It is true that the BBC and Sky News projections of what the national share of the vote would have been, if the whole country had voted, put the two main parties neck and neck. It is also true that if such vote shares were replicated in a general election, the Tories and DUP would be unable to form a government – they would need at least the Liberal Democrats (Sky News) if not the SNP as well (BBC).

There are too many ifs in that chain of reasoning to sustain the conclusion that Corbyn is on his way to No 10.

Corbyn’s spin doctors should simply say that neck and neck with the Tories was a lot better than last year’s local elections, when Labour was nine points behind. And they should point out that Labour closed most of that gap during the five-week general election campaign that followed.

That is why attempts by Corbyn supporters to twist the facts to portray Thursday’s results as better than they were are so pointless. All they have to say is: We started the 2017 general election campaign 20 points behind and ended up depriving May of her majority. Jeremy has super powers and you lot always underestimate him.

Which is why the Conservative spin operation was smart. All it took was one party spokesperson to say that Corbyn was “past his peak”. It was a mild observation that chimed with what several commentators were already saying. But it helps to feed the idea that Corbyn has had his moment and is on the slide from now on.

Statistically, it is plausible. In local elections, Corbyn did best in 2016, when Labour’s projected national share of the vote was one point ahead of the Tories’. In national opinion polls, Labour peaked at around 44 per cent in the month after the 2017 general election. It has since drifted down to around 40 per cent, with the Tories just ahead. Labour Party membership, one of the most remarkable aspects of the Corbyn phenomenon, is still high, at 546,000, but below the peaks of 552,000 in June 2017 and January 2018.

The four years until the next general election is a long time to keep up the enthusiasm and unity of a movement built so much on being different from anything that has gone before. By 2022 Corbyn will have been leader for seven years, and will have had to take more positions that will disappoint some of his supporters, such as becoming a privy counsellor, supporting Brexit or admitting antisemitism is a problem for the party.

And the one thing we know about the next election is that it won’t be like the last. For one thing, if a Labour minority government propped up by the Lib Dems and SNP seemed a likely outcome, the campaign might play out more like Ed Miliband’s did in 2015.

None of the three factors behind Labour’s 2017 campaign surge are likely to be repeated. One was the dementia tax; another was Theresa May’s wooden, people-phobic campaigning; a third was many voters’ surprise at discovering Corbyn wasn’t a monster.

Labour can still win. Anything can happen in politics. Phase 1 Corbyn has peaked, and is now on a gently declining plateau. But Labour could find new ways to gain support – or the Tories could find new ways to lose it.